Characterisation of materials and objects based on an optical response by the objects when irradiated by a suitable irradiation source is widely spread in the biophysical, biochemical and biopharmaceutical fields. Some examples thereof are dynamic light scattering, single molecule spectroscopy or single particle tracking microscopy. In fluorescence single particle tracking (fSPT), for example, fluorescence light emitted by fluorescent particles upon irradiation by an excitation source is detected by a fluorescence microscope and a digital camera. By imaging the movement of the particles when dispersed in a solution, it is possible to calculate the diffusion coefficient and hence the size of the individual particles. Such experiments are typically based on normal epi-fluorescence illumination, providing a low signal to background ratio due to out of focus fluorescence which can reach the detector because of a limited confinement of the excitation beam and the detection volume. Basically two strategies have been proposed to avoid light from reaching the detector that is coming from other parts of the sample than the actual focal plane. The first strategy is based on increasing the confinement of the detection volume. This is being used in the classic field of confocal microscopy. The second strategy is based on increasing the confinement of the excitation volume. This is the basic motivation for multi-photon microscopy where excitation of fluorophores will only occur in the focal spot of the focused laser beam, which has a volume of less than a femto-liter. Imaging of the sample is then achieved by scanning the laser focus across the sample in a raster pattern, hence limiting the maximal image acquisition rate. Another solution is provided by Ritter et al. Ritter et al. describe in Optics Express 16 (2008) page 7142 a high resolution selective plane illumination microscope whereby confinement along the optical axis of the detection path is achieved by illuminating the sample from the side with a thin plane or sheet of light. The selective plane excitation, which could also be referred to as sheet illumination, allows reduction of the background noise due to the fact that no excitation is performed in parts of the object not of interest. Reduction of background noise results in a significantly higher contrast, which results in an improved detection sensitivity. The selective plane excitation as described is created by creating a sheet like illumination using a set of optical elements including a cylindrical beam expander combined with an objective lens for generating a sheet like illumination.